The present invention relates to an apparatus of driving a multi-layer recording optical disk, more specifically, to technology of adjusting a sensitivity dispersion of an actuator during layer jumping, in which an objective lens is moved in a focusing direction, so as to perform a focus servo operation on an arbitrary recording layer.
In recent years, an optical disk called a DVD has been popularized as a large capacity recording medium. The DVD has two recording layers at a maximum in one surface and is capable of recording at both surfaces. In a reproducing apparatus (optical disk apparatus) for such multi-layer recording optical disk, reproduction of a layer may be required while the focus servo operation is performed on the other recording layer which is being reproduced. Therefore, the optical disk apparatus requires a control function (layer jumping function) to control a distance in a focusing direction between the objective lens and the optical disk so that the focus servo operation may be performed on a target layer.
In order to realize the focus servo operation and layer jumping, an actuator is employed in the optical disk apparatus. The actuator functions as a driving mechanism of freely changing a facing direction of the objective lens to the focusing direction, the objective lens converging a laser beam on the recording layer of the optical disk. This actuator is provided to an optical pickup which houses the objective lens.
In the optical pickup, the circumference of the objective lens is provided with a coil portion, which is supported by springs or the like so as to be vertically (in the focusing direction) displaced. In the optical disk apparatus, when layer jumping is conducted at the time of reproducing the optical disk or the like, the focus servo operation is turned off and then a kick voltage is applied to the coil for a predetermined time, so that the objective lens is started to move in a direction of a target layer. When a focal point of the objective lens is moved close to the target layer, a brake voltage is applied to the coil for a predetermined time to stop movement of the objective lens, and then, data reproduction of the target layer is conducted by performing the focus servo operation.
In general, there arises a sensitivity dispersion of the actuator of the optical pickup in the focus direction, and such dispersion is caused by an individual difference of the optical pickup, characteristic changes of the actuator with the elapse of time, and also by change in magnetic force of a magnet caused by environmental changes in temperature, humidity and the like. This sensitivity dispersion of the actuator may cause dispersions of a moving speed and a moving distance of the objective lens in the focusing direction with respect to a kick voltage and a brake voltage applied to the coil of the actuator.
Thus it is desirable to adjust the sensitivity dispersion of the actuator in order to improve stability and convergence in layer jumping.
An object of the present invention is to provide technology for adjusting the sensitivity dispersion of the actuator in the optical pickup during layer jumping.
In order to solve the problem, according to one aspect of the present invention, there is provided a method of controlling movement of an objective lens in an optical disk apparatus. In the method, a time for moving a focal point of an objective lens between a surface and a recording layer of a multi-layer recording optical disk is measured by moving the objective lens for converging a laser beam in a focusing direction to observe a reflected light from the optical disk while emitting the laser beam to the optical disk. When a recording layer on which the laser beam is to be converged is required to be changed at the time of scanning the optical disk, the objective lens is moved by use of a signal for driving the objective lens toward the recording layer, on which the laser beam is to be converged, and a signal for braking the objective lens. Such signals are separately defined based on a ratio of the measured time and a predetermined reference time.
Further, in order to solve the above problem, according to another aspect of the present invention, there is provided an optical disk apparatus of driving a multi-layer recording optical disk. The optical disk apparatus includes a portion for measuring a time for moving a focal point of an objective lens between a surface and a recording layer of the multi-layer recording optical disk by moving the objective lens for converging a laser beam in a focusing direction to observe a reflected light from the optical disk while emitting the laser beam to the optical disk; and a controlling portion for moving the objective lens by use of a signal for driving the objective lens toward a recording layer on which the laser beam is to be converged and a signal for braking the objective lens, when the recording layer, on which the laser beam is to be converged, is required to be changed at the time of scanning the optical disk. The signals are separately defined based on a ratio of the measured time to a predetermined reference time.